1. FIELD OF THE INVENTION
The present invention relates to an image forming apparatus for printing and copying apparatus using electrophotographic processes.
2. DESCRIPTION OF THE RELATED ART
Conventional image forming apparatus for printers and the like control the amount of toner supplied to the developing devices to maintain a constant toner density within the developing material, and adjust the electric charging potential and developing bias voltage so as to maintain image quality, particularly uniform image density. Due to the aforesaid type of image density control, a reference electrostatic latent image pattern is formed outside of the effective image formation region on the surface of the photosensitive drum for the purpose of density detection, said reference latent image pattern is developed to produce a visible toner image of the reference latent image, i.e., a reference density pattern image. The density of the reference density pattern image is detected by means of a density detecting sensor of a reflecting type comprising a photoemitter element and a photoreceptor element, such that the amount of toner supplied to the developing devices can be controlled in accordance with the aforesaid reference density detection.
Conventional methods, however, use only the image density criterium in maintaining uniform image quality, and do not consider image resolution. Conventional methods, therefore, do not resolve the problem that line images, e.g., characters and lines and the like become thinner and thicker due to the effects of photosensitive drum deterioration and the like.